This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-065104, filed Mar. 9, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a silver halide photographic emulsion and, more particularly, to a silver halide photographic emulsion containing silver halide grains by which deterioration by oxygen is improved, and a silver halide photographic light-sensitive material containing the emulsion.
In silver halide photographic emulsions, improving the sensitivity/graininess ratio is the most important object.
As a method of improving the sensitivity/graininess ratio of a silver halide photographic emulsion, the use of tabular grains which increase the efficiency of light absorption is known in, e.g., U.S. Pat. No. 4,956,269. The sensitivity can be improved by increasing the aspect ratio of such tabular grains and increasing the amount of a spectral sensitizing dye. Reduction sensitization is also known as a method of increasing the grain sensitivity.
Improving the sensitivity, however, often lowers the resistance against deterioration of a light-sensitive material during storage. In particular, oxygen participates in an increase in fog during storage, so it is strongly desired to improve this fog increase.
As a method of improving the fog increase caused by oxygen, it is possible to use a radical scavenger which deactivates oxygen or organic radicals generated in a light-sensitive material by oxygen. Examples are phenol-based compounds described in, e.g., Jpn. Pat. Appln. KOKAI PUBLICATION No. (hereinafter referred to as JP-A-)7-72599 and hydroxyamine-based compounds represented by, e.g., formulas (A-I) to (A-III) described in JP-A-8-76311 and U.S. Pat. No. 5,719,007, formula (S2) described in JP-A-10-10668, formula (S1) described in JP-A-11-15102, and formula (S1) described in JP-A-10-90819.
JP-A""s-9-96883 and 11-153840 have disclosed methods of preparing tabular grains in the presence of an oxidizer for silver, but do not predict a reduction of fog by a halogen oxoacid salt of the present invention. Also, Jpn. Pat. Appln. KOKOKU PUBLICATION No. (hereinafter referred to as JP-B-)52-14625 has disclosed a method of intensifying dye images in the presence of a chlorite. However, unlike the present invention JP-B-52-14625 does not describe any method of using the chlorite during the preparation of emulsions.
It is an object of the present invention to provide a silver halide emulsion in which changes in fog caused by oxygen during storage are significantly improved without lowering the sensitivity, and a silver halide photographic light-sensitive material containing the emulsion.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The present inventors made extensive studies and have found a means for maintaining improved sensitivity and suppressing an increase in fog by oxygen. Specifically, the present inventors have found a means to previously remove fine silver nuclei, which exist on the surface or in the interior of an emulsion grain and presumably cause oxygen fog, by the use of an oxidizer.
That is, the object of the present invention is achieved by silver halide photographic emulsions described below and a silver halide photographic light-sensitive material using the emulsions.
(1) A silver halide photographic emulsion comprising silver halide grains, wherein the emulsion was prepared in the presence of at least one halogen oxoacid salt represented by formula (I) below:
M(XOn)mxe2x80x83xe2x80x83Formula (I)
wherein M represents an alkali metal ion or alkaline-earth metal ion, x represents a halogen atom, n represents 2 or 3, and m represents 1 or 2.
(2) The silver halide photographic emulsion described in item (1) above, wherein the halogen oxoacid salt is chlorite.
(3) The silver halide photographic emulsion described in item (1) or (2) above, wherein 50% or more of the total projected area of all the silver halide grains contained in the emulsion is occupied by tabular silver halide grains, each having (111) faces as parallel main planes and an aspect ration of 5 or more.
(4) The silver halide photographic emulsion described in any one of items (1) to (3) above, wherein the emulsion was reduction sensitized by at least one reduction sensitizer selected from a group consisting of (a) thiourea dioxide, (b) hydroxyamines and their derivatives, and (c) dihydroxybenzenes and their derivatives.
(5) A silver halide photographic light-sensitive material having at least one silver halide emulsion layer on a support, wherein the silver halide photographic emulsion described in any one of items (1) to (4) above is contained in the at least one silver halide emulsion layer.
The present invention will be described in detail below.
First, details of a halogen oxoacid salt represented by formula (I) will be described.
The halogen atom represented by X is preferably chlorine, bromine, or iodine, and more preferably, chlorine. The halogen oxoacid salt is preferably chlorite, bromate, or iodate, and most preferably, chlorite.
The alkali metal ion or alkaline-earth metal ion represented by M is preferably a potassium ion, sodium ion, magnesium ion, or calcium ion, and more preferably, a sodium ion.
Practical examples of a halogen oxoacid salt defined in the present invention are sodium chlorite, potassium chlorite, potassium iodate, and sodium bromate. However, the present invention is not limited to these examples.
The halogen oxoacid salt can be used in any one of silver halide grain emulsion preparing steps. The halogen oxoacid salt can be added once or can be added two or more times separately during the emulsion preparing steps. The halogen oxoacid salt preferably be added once or more times during the preparing process that is selected from during silver halide grain formation, after silver halide grain formation and before the start of a desilvering step, during the desilvering step, before the start of chemical ripening, and during the chemical ripening step. The halogen oxoacid salt is more preferably added at least once during the emulsion preparing process that is selected from during grain formation and before the start of chemical ripening, during the chemical ripening step, and after the completion of the chemical ripening. When a silver halide emulsion is to be reduction-sensitized by using a reducing agent as will be described later, the halogen oxoacid salt is preferably added. It is unpreferable to add the halogen oxoacid salt when a coating solution is prepared using a silver halide emulsion already chemically ripened after grain formation, because the effect of the present invention is impaired.
The concentration of the halogen oxoacid salt in a step in which it is used is preferably 1xc3x9710xe2x88x926 to 1xc3x9710xe2x88x923 mol, and more preferably, 5xc3x9710xe2x88x926 to 2xc3x9710xe2x88x924 mol per mol of silver halide.
Two or more types of the halogen oxoacid salts can be used together.
The halogen oxoacid salt is preferably added in the form of an aqueous solution or aqueous gelatin solution. When the halogen oxoacid salt is used as an aqueous solution, the pH is preferably adjusted by a known buffering agent. The pH is preferably 6 to 10, and more preferably, 7 to 9.5.
Silver halide emulsion of the present invention will be described in detail below.
Silver halide grains contained in the emulsion of the present invention have regular crystals such as cubic, octahedral, or tetradecahedral crystals, irregular crystals such as spherical or tabular crystals, crystals having crystal defects such as twin planes, or composite shapes thereof. Silver halide grain emulsions are particularly preferably tabular grains.
In the photographic emulsion of the invention, 50% or more of the total projected area are preferably accounted for by tabular grains, each having an aspect ratio of 5 or more (hereinafter, this emulsion is also referred to as xe2x80x9ctabular grain emulsionxe2x80x9d). The projected area and aspect ratio of a tabular grain can be measured from an electron micrograph obtained by shadowing the tabular grain together with a reference latex sphere by using a carbon replica method. When viewed in a direction perpendicular to the main planes, a tabular grain commonly has the shape of a hexagon, triangle, or circle. The aspect ratio is the value obtained by dividing the diameter (equivalent-circle diameter) of a circle having an area equal to the projected area of a tabular grain by the thickness of the grain. As the shape of a tabular grain, the ratio of hexagons is preferably as high as possible. Also, the ratio of the lengths of adjacent sides of the hexagon is preferably 1:2 or less.
The higher the aspect ratio, the more remarkable the effect of the present invention. Therefore, in the photographic emulsion of the invention, it is more preferable that 50% or more of the total projected area are accounted for by tabular grains having an aspect ratio of 8 or more, and more preferably, 12 or more. If the aspect ratio is too high, however, the variation coefficient of the grain size distribution increases. Therefore, an aspect ratio of 50 or less is usually preferred.
The average grain diameter of silver halide grains contained in the emulsion of the present invention is preferably 0.2 to 10.0 xcexcm, and more preferably, 0.5 to 5.0 xcexcm as an average equivalent-circle diameter. The equivalent-circle diameter is the diameter of a circle having an area equal to the projected area of the parallel main planes of a grain. The projected area of a grain can be obtained by measuring the area on an electron micrograph and correcting the photographing magnification. The average equivalent-sphere diameter is preferably 0.1 to 5.0 xcexcm, and more preferably, 0.6 to 2.0 xcexcm. In these ranges, the sensitivity/graininess ratio of a photographic emulsion is highest. The average thickness of tabular grains is preferably 0.05 to 1.0 xcexcm. The average equivalent-circle diameter is the average value of the equivalent-circle diameters of 1,000 or more grains randomly sampled from a homogeneous emulsion. The same can be applied to the average thickness.
The grain size distribution of silver halide grains contained in the emulsion of the present invention can be either monodisperse or polydisperse, but is preferably monodisperse.
The tabular grain is preferably composed of opposing (111) main planes and side faces connecting these main planes. At least one twin plane preferably exists between the main planes. In a tabular grain used in the present invention, two twin planes are preferably observed. As described in U.S. Pat. No. 5,219,720, the spacing between these two twin planes can be decreased to less than 0.012 xcexcm. Also, as described in JP-A-5-249585, the value obtained by dividing the distance between the (111) main planes by the twin plane spacing can be increased to 15 or more.
In the present invention, 75% or less of all side faces connecting the opposing (111) main planes of the tabular grain are particularly preferably constituted by (111) faces. xe2x80x9c75% or less of all side faces are constituted by (111) facesxe2x80x9d means that in a tabular grain, crystallographic faces other than (111) faces exist at a ratio higher than 25% of all side faces. It is generally understood that this face is a (100) face, but some other face such as a (110) face or a higher-index face also can exist. The effect of the present invention is more remarkable when 70% or less of all side faces are constituted by (111) faces.
Whether 70% or less of all side faces are constituted by (111) faces can be readily determined from a shadowed electron micrograph of the tabular grain obtained by a carbon replica method. When 75% or more of side faces are constituted by (111) faces in a hexagonal tabular grain, six side faces directly connecting to the (111) main planes alternately connect at acute and obtuse angles to the (111) main planes. On the other hand, when 70% or less of all side faces are constituted by (111) faces in a hexagonal tabular grain, all six side faces directly connecting to the (111) main planes connect at obtuse angles to the (111) main planes. By performing shadowing at an angle of 500 or less, it is possible to distinguish between obtuse and acute angles of side faces with respect to the main planes. Shadowing at an angle of preferably 10xc2x0 to 30xc2x0 facilitates distinguishing between obtuse and acute angles.
A method using adsorption of sensitizing dyes is also effective to obtain the ratio of (111) faces to (100) faces. The ratio of (111) faces to (100) faces can be quantitatively obtained by using a method described in Journal of Japan Chemical Society, 1984, Vol. 6, pp. 942 to 947. By using this ratio and the equivalent-circle diameter and thickness of a tabular grain, it is possible to calculate the ratio of (111) faces in all side faces. In this case it is assumed that a tabular grain is a circular cylinder and the use is made of the equivalent-circle diameter and thickness. On the basis of this assumption, the ratio of side faces to the total surface area can be obtained. The value obtained by dividing the ratio of (100) faces, which is obtained by adsorption of sensitizing dyes as described above, by the ratio of side faces and multiplying the quotient by 100 is the ratio of (100) faces in all side faces. By subtracting this value from 100, the ratio of (111) faces in all side faces can be calculated. In the present invention, the ratio of (111) faces in all side faces is more preferably 65% or less.
A method by which 75% or less of all side faces of the tabular grain of the present invention are constituted by (111) faces will be described below. Most generally, the ratio of (111) faces in side faces of a silver iodobromide or silver bromochloroiodide tabular grain can be determined by the pBr during the preparation of the tabular grain emulsion. The pBr is the logarithm of the reciprocal of the Brxe2x88x92 ion concentration of a system. The pBr is preferably so set that, assuming the total silver amount of a tabular grain emulsion is 100, the ratio of (111) faces in side faces decreases, i.e., the ratio of (100) faces in side faces increases, after at least 70% of the total silver amount are added. The pBr is most preferably so set that the ratio of (100) faces in side faces increases after at least 90% of the total silver amount are added.
If the pBr is so set that the ratio of (100) faces in side faces increases before 70% of the total silver amount are added, the aspect ratio of a tabular grain undesirably lowers. If the pBr is so set that the ratio of (100) faces in side faces increases after 98% or more of the total silver amount are added, it becomes difficult to achieve the (100) face ratio in side faces by which the effect of the present invention is obtained. Accordingly, the effect of the present invention is most remarkably obtained when the pBr is so set that the ratio of (100) faces in side faces increases after at least 90% of the total silver amount are added and before 98% or more of the total silver amount are added. However, as another method it is also possible to increase the ratio of (100) faces in side faces by performing ripening by setting the pBr such that the ratio of (100) faces in side faces increases after the total silver amount is added.
The value of the pBr by which the ratio of (100) faces in side faces increases can vary over a broad range in accordance with the temperature and pH of the system, the type and concentration of a protective colloid agent such as gelatin, and the presence/absence, type, and concentration of a silver halide solvent. Usually, the pBr is preferably 2.0 to 5, and more preferably, 2.5 to 4.5. As described above, however, the value of the pBr can easily change owing to, e.g., the presence of a silver halide solvent. Hence, no silver halide solvent is preferably used in the present invention.
Examples of the silver halide solvent usable in the present invention are (a) organic thioethers described in, e.g., U.S. Pat. Nos. 3,271,157, 3,531,289, and 3,574,628, and JP-A""s-54-1019 and 54-158917, (b) thiourea derivatives described in, e.g., JP-A""s-53-82408, 55-77737, and 55-2982, (c) a silver halide solvent having a thiocarbonyl group sandwiched between an oxygen or sulfur atom and a nitrogen atom described in JP-A-53-144319, (d) imidazoles described in JP-A-54-100717, all the disclosures of which are incorporated herein by reference (e) ammonia, and (f) thiocyanate.
Particularly preferable solvents are thiocyanate, ammonia, and tetramethylthiourea. Although the amount of a solvent used changes in accordance with the type of the solvent, a preferred amount of, e.g., thiocyanate is 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x922 mol per mol of a silver halide.
EP515894A1, the disclosure of which is incorporated herewith by reference, and the like can be referred to as a method of changing the face index of a side face of a tabular grain emulsion. Also, polyalkyleneoxide compounds described in, e.g., U.S. Pat. No. 5,252,453, the disclosure of which is incorporated herewith by reference, can be used. It is effective to use face index modifiers described in, e.g., U.S. Pat. Nos. 4,680,254, 4,680,255, 4,680,256, and 4,684,607, the disclosures of which are incorporated herewith by reference. Common photographic spectral sensitizing dyes also can be used as face index modifiers.
In the present invention, the tabular grain emulsion can be prepared by diverse methods as long as the aforesaid required conditions are met. The preparation of the tabular grain emulsion basically includes three steps of nucleation, ripening, and growth. In the nucleation step of the tabular grain emulsion of the present invention, it is extremely effective to use gelatin having a small methionine content described in U.S. Pat. Nos. 4,713,320 and 4,942,120, perform nucleation at high pBr described in U.S. Pat. No. 4,914,014, and perform nucleation within short time periods described in JP-A-2-222940, the disclosures of which are incorporated herewith by reference. In the ripening step of the tabular grain emulsion of the present invention, it is sometimes effective to perform ripening in the presence of a low-concentration base described in U.S. Pat. No. 5,254,453 and perform ripening at high pH described in U.S. Pat. No. 5,013,641, the disclosures of which are incorporated herewith by reference. In the growth step of the tabular grain emulsion of the present invention, it is particularly effective to perform growth at low temperature described in U.S. Pat. No. 5,248,587 and use fine silver iodide grains described in U.S. Pat. Nos. 4,672,027 and 4,693,964, the disclosures of which are incorporated herewith by reference. Additionally, it is preferable to perform growth by adding silver bromide, silver iodobromide, and silver bromochloroiodide fine grain emulsions, thereby effect ripening. It is also possible to supply these fine grain emulsions by using a stirring device described in JP-A-10-43570.
In the emulsions of the present invention, it is preferable to introduce positive hole capturing silver nuclei by intentional reduction sensitization. xe2x80x9cIntentional reduction sensitizationxe2x80x9d means reduction sensitization performed by adding a reduction sensitizer. A positive hole capturing silver nucleus is a small silver nucleus having a little development activity. This silver nucleus can prevent recombination loss in the exposure step and increase the sensitivity. Positive hole capturing silver nuclei can be introduced by performing intentional reduction sensitization during the formation of silver halide emulsion grains.
As the reduction sensitizer, stannous chloride, ascorbic acid and its derivatives, amines and polyamines, hydrazine derivatives, thiourea dioxide, silane compounds, borane compounds, dihydroxybenzenes and their derivatives, and hydroxyamines and their derivatives are effective. In reduction sensitization performed for the emulsion of the present invention, it is possible to selectively use these reduction sensitizers or to use two or more types of compounds together. Preferred reduction sensitizers in the present invention are thiourea dioxide, hydroxyamines and their derivatives, and dihydroxybenzenes and their derivatives. Although the addition amount of reduction sensitizers must be so selected as to meet the emulsion preparing conditions, a proper amount is 10xe2x88x927 to 10xe2x88x92mol per mol of a silver halide.
Reduction sensitizers are dissolved in water or a solvent, such as alcohols, glycols, ketones, esters, or amides, and the resultant solution is added during grain growth.
In the present invention, positive hole capturing silver nuclei are preferably formed by adding reduction sensitizers after 50% of the total silver amount required for grain formation are added. More preferably, positive hole capturing silver nuclei are formed by adding reduction sensitizers after 70% of the total silver amount required for grain formation are added. In the present invention, positive hole capturing silver nuclei can also be formed at the surface of the grain by adding reduction sensitizers after grain formation is completed.
When reduction sensitizers are added during grain formation, some silver nuclei formed can stay inside a grain, but some ooze out to form silver nuclei on the grain surface. In the present invention, these oozing silver nuclei are preferably used as positive hole capturing silver nuclei.
The dihydroxybenzenes and their derivatives that are preferable as a reduction sensitizer are compounds represented by general formula (V-1) and/or compounds represented by general formula (V-2) below: 
In formulas (V-1) and (V-2), each of W51 and W52 independently represents a sulfo group or hydrogen atom. However, at least one of W51 and W52 represents a sulfo group. A sulfo group is generally an alkali metal salt such as sodium or potassium or a water-soluble salt such as ammonium salt. Favorable practical examples are disodium 4,5-dihydroxybenzene-1,3-disulfonate, 4-sulfocatechol ammonium salt, 2,3-dihydroxy-7-sulfonaphthalene sodium salt, and 2,3-dihydroxy-6,7-disulfonaphthalene potassium salt. Most preferable compound is disodium 4,5-dihydroxybenzene-1,3-disulfonate. A preferred addition amount can vary in accordance with, e.g., the temperature, pBr, and pH of the system to which the compound is added, the type and concentration of a protective colloid agent such as gelatin, and the presence/absence, type, and concentration of a silver halide solvent. Generally, the addition amount is preferably 0.0005 to 0.5 mol, and more preferably, 0.003 to 0.05 mol per mol of a silver halide.
The hydroxyamines and their derivatives that are preferable for a reduction sensitizer is represented by general formula (A) below:
Raxe2x80x94N(Rb)OHxe2x80x83xe2x80x83(A)
In the formula (A), Ra represents an alkyl group, alkenyl group, aryl group, acyl group, carbamoyl group, sulfamoyl group, alkoxycarbonyl group, aryloxycarbonyl group or hetero cyclic group; and Rb represents a hydrogen atom or one of the groups represented by Ra.
Ra may be further substituted by at least one substituent. Examples of the substituent are an alkyl group, alkenyl group, aryl group, hetero cyclic group, hydroxy group, alkoxy group, aryloxy group, alkylthio group, arylthio group, amino group, acylamino group, sulfonamide group, alkylamino group, arylamino group, carbamoyl group, sulfamoyl group, sulfo group, carboxyl group, halogen atom, cyano group, nitro group, sulfonyl group, acyl group, alkoxycarbonyl group, aryloxy carbonyl group, acyloxy group, and hydroxylamine group. Ra is preferably a hetero cyclic group, for example, 1,3,5-triazine-2-yl, 1,2,4-triazine-3-yl, pyridine-2-yl, pyrazinyl, pyrimidinyl, purinyl, quinolyl, imidazolyl, thiazolyl, oxazoly, 1,2,4-triazol-3-yl, benzimidazol-2-yl, benzothiazolyl, benzoxyazolyl, thienyl, furyl, imidazolydinyl, pyrolinyl, tetrahydrofuryl, morpholinyl, and phosphinophosphorous-2-yl.
Rb is preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or a methyl group.
Practical examples of the compounds represented by general formula (A) are those of RS-I to RS-X set forth below, however, the hydroxyamines and their derivatives that can be used in the present invention are not limited to these: 
An emulsion of the present invention is preferably silver iodobromide, silver iodochloride, silver chlorobromide, or silver bromochloroiodide, and more preferably, silver iodobromide or silver bromochloroiodide. Silver bromochloroiodide can contain silver chloride, and the silver chloride content is preferably 8 mol % or less, and more preferably, 3 to 0 mol %. The silver iodide content is preferably 20 mol % or less because the variation coefficient of the grain size distribution is favorably 25% or less. Lowering the silver iodide content facilitates decreasing the variation coefficient of the grain size distribution of a tabular grain emulsion. It is particularly preferable that the variation coefficient of the grain size distribution of a tabular grain emulsion be 20% or less and the silver iodide content be 10 mol % or less. The variation coefficient of the silver iodide content between grains is preferably 20% or less, and particularly preferably, 10% or less, regardless of the silver iodide content.
An emulsion of the present invention preferably has a structure with respect to the silver iodide distribution in a grain. This structure of the silver iodide distribution can be a double structure, triple structure, quadruple structure, or higher-order structure.
The silver iodide content on the grain surface of an emulsion of the present invention is preferably 10 mol % or less, and more preferably, 5 mol % or less. The silver iodide content on the grain surface defined in the present invention is measured by using XPS (X-ray Photoelectron Spectroscopy). The principle of XPS used in the analysis of the silver iodide content near the surface of a silver halide grain is described in Aihara et al., xe2x80x9cSpectra of Electronsxe2x80x9d (Kyoritsu Library 16: issued Showa 53 by Kyoritsu Shuppan). A standard measurement method of XPS is to use Mg-Kxcex1 as excitation X-rays and measure the intensities of photoelectrons (usually I-3d5/2 and Ag-3d5/2) of iodine (I) and silver (Ag) released from silver halide grains in an appropriate sample form. The content of iodine can be calculated from a calibration curve of the photoelectron intensity ratio (intensity (I)/intensity (Ag)) of iodine (I) to silver (Ag) formed by using several different standard samples having known iodine contents. XPS measurement for a silver halide emulsion must be performed after gelatin adsorbed by the surface of a silver halide grain is decomposed by, e.g., proteinase and removed. A tabular grain emulsion used in the present invention in which the silver iodide content on the grain surface is 5 mol % or less is an emulsion whose silver iodide content is 5 mol % or less when emulsion grains contained in the emulsion are analyzed by XPS. If obviously two or more types of emulsions are mixed, appropriate preprocessing such as centrifugal separation or filtration must be performed before one type of emulsion is analyzed.
The structure of an emulsion of the present invention is preferably a triple structure including silver bromide/silver iodobromide/silver bromide or a higher-order structure. The boundary of the silver iodide content between layers of the structure can be a distinct boundary or can continuously moderately change. In the measurement of the silver iodide content using a powder X-ray diffraction method, the silver iodide content does not have two distinct peaks but shows an X-ray diffraction profile having a tail in the direction of a high silver iodide content.
In the present invention, the silver iodide content of a phase inside the surface is preferably higher than the silver iodide content on the surface. This silver iodide content of a phase inside the surface is higher, preferably by 5 mol % or more, and more preferably, by 7 mol % or more.
Emulsion grains of the present invention are preferably spectrally sensitized by a known cyanine dye. Although the cyanine sensitizing dye can be added in any step of the emulsion preparing process, spectral sensitization is preferably performed by adding the cyanine dye during or before chemical sensitization.
An example of a cyanine dye useful in the present invention is a dye represented by formula (II):
An example of a cyanine dye useful in the present invention is a dye represented by formula (II): 
wherein each of Z1 and Z2 independently represents an atomic group necessary to form a heterocyclic nucleus commonly used in a cyanine dye. Examples are thiazole, thiazoline, benzothiazole, naphthothiazole, oxazole, oxazoline, benzoxazole, naphthoxazole, tetrazole, pyridine, quinoline, imidazoline, imidazole, benzoimidazole, naphthoimidazole, selenazoline, selenazole, benzoselenazole, naphthoselenazole, and indolenine. These heterocyclic nuclei can be substituted by, e.g., a lower alkyl group such as methyl, halogen atom, phenyl. group, hydroxyl group, 1- to 4-carbon alkoxy group, carboxyl group, alkoxycarbonyl group, alkylsulfamoyl group, alkylcarbamoyl group, acetyl group, acetoxy group, cyano group, trichloromethyl group, trifluoromethyl group, or nitro group.
Each of L1 and L2 independently represents an unsubstituted or substituted methine group. Examples of this substituted methine group are methine groups substituted by a lower alkyl group such as methyl or ethyl, phenyl, substituted phenyl, methoxy, and ethoxy. If both L1 and L2 are substituted methine groups, these substituents can combine to form a ring.
Each of R1 and R2 independently represents a 1- to 5-carbon alkyl group; a substituted alkyl group having a carboxy group: e.g., carboxymethyl and 3-carboxybutyl; a substituted alkyl group having a sulfo group: e.g., a substituted alkyl group having a sulfo group such as xcex2-sulfoethyl, xcex3-sulfopropyl, xcex4-sulfobutyl, xcex3-sulfobutyl, 2-(3-sulfopropoxy)ethyl, 2-[2-(3-sulfopropoxy)ethoxy]ethyl, or 2-hydroxyxc2x7sulfopropyl, or an allyl group or a substituted alkyl group commonly used in an N-substituent of a cyanine dye. X1xe2x88x92 represents an acid anion group, e.g., an iodine ion, bromine ion, p-toluenesulfonic acid ion, or perchloric acid ion. n1 represents 1 or 2. n1 is 1 when the compound takes a betaine structure. m1 represents 1, 2, or 3.
Representative compounds of effective spectral sensitizing dyes used in the present invention are presented below. However, the present invention is not limited to these examples. 
Although these sensitizing dyes can be used singly, combinations of these sensitizing dyes can also be used. Combinations of sensitizing dyes are often used for a supersensitization purpose. Representative examples of combinations are described in U.S. Pat. Nos. 2,688,545, 2,977,229, 3,397,060, 3,522,052, 3,527,641,3,617,293, 3,628,964, 3,666,480, 3,672,898, 3,679,428, 3,703,377, 3,769,301,3,814,609, 3,837,862, and 4,026,707, British Patent Nos. 1,344,281 and 1,507,803, JP-B""s-43-4936 and 53-12375, and JP-A""s-52-110618 and 52-109925, the disclosures of which are incorporated herein by reference.
In the present invention, two or more types of cyanine dyes selected from cyanine dyes represented by formula (II) can be added.
A cyanine dye represented by formula (II) is more preferably a monomethinecyanine dye.
In addition to sensitizing dyes, emulsions can also contain dyes having no spectral sensitizing effect or substances not essentially absorbing visible light and presenting supersensitization.
Sensitizing dyes can be added to the emulsion at any point conventionally known to be useful during emulsion preparation. Most ordinarily, the addition is performed after completion of chemical sensitization and before coating. However, it is possible to perform the addition at the same timing as addition of chemical sensitizing dyes to perform spectral sensitization and chemical sensitization simultaneously, as described in U.S. Pat. Nos. 3,628,969 and 4,225,666. It is also possible to perform the addition prior to chemical sensitization, as described in JP-A-58-113928, or before completion of formation of a silver halide grain precipitation to start spectral sensitization. Alternatively, as disclosed in U.S. Pat. No. 4,225,666, these compounds can be added separately; a portion of the compounds may be added prior to chemical sensitization, while the remaining portion is added after that. That is, the compounds can be added at any timing during formation of silver halide grains, including the method disclosed in U.S. Pat. No. 4,183,756.
The amount of sensitizing dyes added to silver halide grains used in the present invention is preferably 5xc3x9710xe2x88x924 mol or more per mol of a silver halide. When the average silver halide grain size is 1.0 to 3.0 xcexcm, an addition amount of about 2xc3x9710xe2x88x924 to 5xc3x9710xe2x88x923 mol is more effective.
The emulsion of the present invention is preferably prepared in the presence of a water-soluble radical scavenger.
A radical scavenger that can be used in the present invention is a compound which, when a 0.05 mmoldmxe2x88x923 ethanol solution of garvinoxyl and a 2.5 mmoldmxe2x88x923 ethanol solution of a test compound are mixed at 25xc2x0 C. by a stopped flow method and changes in the absorbance with time at 430 nm are measured, substantially decolors the garvinoxyl (reduces the absorbance at 430 nm). (If dissolution is impossible at the above concentration, measurement can be performed at a lower concentration.)
The radical scavenge rate of a radical scavenger usable in the present invention is the decoloration rate constant of garvinoxyl obtained by the above method. A radical scavenger preferably has a radical scavenge rate of 0.01 mmolsxe2x88x921dm3 or more, and more preferably, 0.1 to 10 mmolsxe2x88x921dm3. A method of obtaining the radical scavenge rate by using garvinoxyl is described in Microchemical Journal 31, pp. 18 to 21 (1985), the disclosure of which is incorporated herewith by reference. A stopped flow method is described in, e.g., Spectroscopy Research Vol. 19, No. 6 (1970), p. 321, the disclosure of which is incorporated herewith by reference.
The solubility to water of the radical scavenger is represented by the distribution coefficient of an n-octanol/water system defined by:
log P=log [(Rs)octanol/(Rs)water]
where (Rs) is the radical scavenger concentration, and (Rs)octanol and (Rs)water are the concentrations in n-octanol and water, respectively.
xe2x80x9cBeing water-solublexe2x80x9d means that the above log P value is smaller than 1.
The distribution coefficient can be calculated by a method described in Journal of Medicinal Chemistry, Vol. 18, No. 9, pp. 865 to 868 (1975).
Examples of the radical scavenger used in the present invention are water-soluble ones of phenol-based compounds described in JP-A-7-72599 and hydroxyamine-based compounds represented by formulas (A-I) to (A-III) described in U.S. Pat. No. 5,719,007, formula (S2) described in JP-A-10-10668, formula (S1) described in JP-A-11-15102, and formula (S1) described in JP-A-10-90819, all the disclosures of which are incorporated herein by reference.
Practical examples of the water-soluble radical scavenger are presented below, but the present invention is not restricted to these examples. 
The above water-soluble radical scavenger is preferably added during emulsion preparation and can be added in any step of the process. For example, the radical scavenger can be added in a silver halide grain formation step, before the start of a desilvering step, in the desilvering step, before the start of chemical ripening, in the chemical ripening step, and before completed emulsion preparation. The radical scavenger can also be separately added a plurality of times in these steps. Preferably, the radical scavenger is added before, during, or after chemical sensitization.
A preferred addition amount of the water-soluble radical scavenger largely depends upon the addition method described above and the type of compound to be added. Generally, the addition amount is preferably 5xc3x9710xe2x88x926 to 0.5 mol, and more preferably, 1xc3x9710xe2x88x925 to 0.005 mol per mol of a photosensitive silver halide. An addition amount larger than the above value is unpreferable because bad influence such as an increase in fog occurs.
Two or more types of radical scavengers can be used together.
The radical scavenger can be added by dissolving it in water or a water-soluble solvent, such as methanol, or ethanol, or in a solvent mixture of these, or can be added by emulsified dispersion. When the radical scavenger is dissolved in water, the pH can be raised or lowered if the solubility rises when the pH is raised or lowered, and the resultant solution can be added. A surfactant can also be present at the same time.
In the present invention, the tabular grains preferably have dislocation lines. The dislocation lines of the tabular grains can be observed by the direct method using a transmission electron microscope at low temperatures as described in, for example, J. F. Hamilton, Phot. Sci. Eng., 11, 57 (1967) and T. Shiozawa, J. Soc. Phot. Sci. Japan, 35, 213 (1972). Illustratively, silver halide grains are harvested from the emulsion with the care that the grains are not pressurized with such a force that dislocation lines occur on the grains, are put on a mesh for electron microscope observation and, while cooling the specimen so as to prevent damaging (printout, etc.) by electron beams, are observed by the transmission method. The greater the thickness of the above grains, the more difficult the transmission of electron beams. Therefore, the use of an electron microscope of high voltage type (at least 200 kV on the grains of 0.25 xcexcm in thickness) is preferred for ensuring clearer observation. The thus obtained photograph of grains enables determining the position and number of dislocation lines in each grain viewed in the direction perpendicular to the principal planes.
The number of dislocation lines of the tabular grains according to the present invention is preferably at least 10 per grain on the average and more preferably at least 20 per grain on the average. When dislocation lines are densely present or when dislocation lines are observed in the state of crossing each other, it happens that the number of dislocation lines per grain cannot accurately be counted. However, in this instance as well, rough counting on the order of, for example, 10, 20 or 30 dislocation lines can be effected, so that a clear distinction can be made from the presence of only a few dislocation lines. The average number of dislocation lines per grain is determined by counting the number of dislocation lines of each of at least 100 grains and calculating a number average thereof.
Dislocation lines can be introduced in, for example, the vicinity of the periphery of tabular grains. In this instance, the dislocation is nearly perpendicular to the periphery, and each dislocation line extends from a position corresponding to x% of the distance from the center of tabular grains to the side (periphery) to the periphery. The value of x preferably ranges from 10 to less than 100, more preferably from 30 to less than 99, and most preferably from 50 to less than 98. In this instance, the figure created by binding the positions from which the dislocation lines start is nearly similar to the configuration of the grain. The created figure may be one which is not a complete similar figure but deviated. The dislocation lines of this type are not observed around the center of the grain. The dislocation lines are crystallographically oriented approximately in the (211) direction. However, the dislocation lines often meander and may also cross each other.
Dislocation lines may be positioned either nearly uniformly over the entire zone of the periphery of the tabular grains or local points of the periphery. That is, referring to, for example, hexagonal tabular silver halide grains, dislocation lines may be localized either only in the vicinity of six apexes or only in the vicinity of one of the apexes. Contrarily, dislocation lines can be localized only in the sides excluding the vicinity of six apexes.
Furthermore, dislocation lines may be formed over regions including the centers of two mutually parallel principal planes of tabular grains. In the case where dislocation lines are formed over the entire regions of the principal planes, the dislocation lines may crystallographically be oriented approximately in the (211) direction when viewed in the direction perpendicular to the principal planes, and the formation of the dislocation lines may be effected either in the (110) direction or randomly. Further, the length of each dislocation line may be random, and the dislocation lines may be observed as short lines on the principal planes or as long lines extending to the side (periphery). The dislocation lines may be straight or often meander. In many instances, the dislocation lines cross each other.
The position of dislocation lines may be localized on the periphery, principal planes or local points as mentioned above, or the formation of dislocation lines may be effected on a combination thereof. That is, dislocation lines may be concurrently present on both the periphery and the principal planes.
In the present invention, dislocation lines are most preferably introduced by adding a sparingly soluble silver halide emulsion to the silver bromide, silver chlorobromide, silver bromochloroiodide, or silver iodobromide tabular emulsion described above. A sparingly soluble silver halide emulsion is more sparingly soluble than the tabular grain emulsion in terms of a halogen composition, and is preferably a silver iodide fine grain emulsion.
In the present invention, dislocation lines are preferably introduced by abruptly adding a silver iodide fine grain emulsion to the tabular grain emulsion described above. This step substantially includes two steps: a step of abruptly adding a silver iodide fine grain emulsion to the tabular grain emulsion, and a step of introducing dislocation lines by growing silver bromide or silver iodobromide. These two steps are sometimes performed completely separately and can also be performed at the same time. Preferably, the steps are performed separately. The first step of rapidly adding a silver iodide fine grain emulsion to the tabular grain emulsion will be described below.
xe2x80x9cRapidly adding a silver iodide fine grain emulsionxe2x80x9d is to add a silver iodide fine grain emulsion within preferably ten minutes, and more preferably, seven minutes. This condition can vary in accordance with the temperature, pBr, and pH of the system to which the emulsion is added, the type and concentration of a protective colloid agent such as gelatin, and the presence/absence, type, and concentration of a silver halide solvent. However, a shorter addition time is more preferable as described above. During the addition, it is preferable that an aqueous solution of silver salt such as silver nitrate be not substantially added. The temperature of the system during the addition is preferably 40xc2x0 C. to 90xc2x0 C., and particularly preferably, 50xc2x0 C. to 80xc2x0 C. The pBr of a silver iodide fine grain emulsion during the addition is not particularly limited.
The silver iodide fine grain emulsion substantially need only be silver iodide and can contain silver bromide and/or silver chloride as long as a mixed crystal can be formed. The emulsion is preferably 100% silver iodide. The crystal structure of silver iodide can be a xcex2 phase, a xcex3 phase, or, as described in U.S. Pat. No. 4,672,026, an a phase or an a phase similar structure. In the present invention, the crystal structure is not particularly restricted but is preferably a mixture of xcex2 and xcex3 phases, and more preferably, a xcex2 phase. The silver iodide fine grain emulsion can be either an emulsion formed immediately before addition described in U.S. Pat. No. 5,004,679 or an emulsion subjected to a regular washing step. In the present invention, an emulsion subjected to a regular washing step is preferably used. The silver iodide fine grain emulsion can be readily formed by a method described in, e.g., aforementioned U.S. Pat. No. 4,672,026. A double-jet addition method using an aqueous silver salt solution and an aqueous iodide salt solution in which grain formation is performed with a fixed pI value is preferred. The pI is the logarithm of the reciprocal of the Ixe2x88x92 ion concentration of the system. The temperature, pI, and pH of the system, the type and concentration of a protective colloid agent such as gelatin, and the presence/absence, type, and concentration of a silver halide solvent are not particularly limited. However, a grain size of preferably 0.1 xcexcm or less, and more preferably, 0.08 xcexcm or less is convenient for the present invention. Although the grain shapes cannot be perfectly specified because the grains are fine grains, the variation coefficient of a grain size distribution is preferably 25% or less. The effect of the present invention is particularly remarkable when the variation coefficient is 20% or less. The sizes and the size distribution of the silver iodide fine grain emulsion are obtained by placing silver iodide fine grains on a mesh for electron microscopic observation and directly observing the grains by a transmission method instead of a carbon replica method. This is because measurement errors are increased by observation done by the carbon replica method since the grain sizes are small. The grain size is defined as the diameter of a circle having an area equal to the projected area of the observed grain. The grain size distribution also is obtained by using this equivalent-circle diameter of the projected area. In the present invention, the most effective silver iodide fine grains have a grain size of 0.07 to 0.02 xcexcm and a grain size distribution variation coefficient of 18% or less.
After the grain formation described above, the silver iodide fine grain emulsion is preferably subjected to regular washing described in, e.g., U.S. Pat. No. 2,614,929, and adjustments of the pH, the pI, the concentration of a protective colloid agent such as gelatin, and the concentration of the contained silver iodide are performed. The pH is preferably 5 to 7. The pI value is preferably the one at which the solubility of silver iodide is a minimum or the one higher than that value. As the protective colloid agent, a common gelatin having an average molecular weight of approximately 100,000 is preferably used. A low-molecular-weight gelatin having an average molecular weight of 20,000 or less also is preferably used. It is sometimes convenient to use a mixture of gelatins having different molecular weights. The gelatin amount is preferably 10 to 100 g, and more preferably, 20 to 80 g per kg of an emulsion. The silver amount is preferably 10 to 100 g, and more preferably, 20 to 80 g, as the amount of silver atoms, per kg of an emulsion. As the gelatin amount and/or the silver amount, it is preferable to choose values suited to the rapid addition of the silver iodide fine grain emulsion.
The addition amount of a silver iodide fine grain emulsion is preferably 1 to 10 mol %, and most preferably, 2 to 7 mol %, as a silver amount, with respect to a tabular grain emulsion. By choosing this addition amount, dislocation lines are preferably introduced, and the effect of the present invention becomes conspicuous. A silver iodide fine grain emulsion is usually dissolved before being added. During the addition it is necessary to sufficiently raise the efficiency of stirring of the system. The rotating speed of stirring is preferably set to be higher than usual. The addition of an antifoaming agent is effective to prevent the formation of foam during the stirring. More specifically, an antifoaming agent described in, e.g., examples of U.S. Pat. No. 5,275,929 is used.
After a silver iodide fine grain emulsion is rapidly added to a tabular grain emulsion, silver bromide or silver iodobromide is grown to introduce dislocation lines. Although the growth of silver bromide or silver iodobromide can be started before or at the same time the addition of a silver iodide fine grain emulsion, the growth of silver bromide or silver iodobromide is preferably started after the addition of a silver iodide fine grain emulsion. The time from the addition of a silver iodide fine grain emulsion to the start of the growth of silver bromide or silver iodobromide is preferably 10 min to 1 sec, more preferably, 5 min to 3 sec, and most preferably, within 1 min. This time interval is preferably as short as possible and is favorably before the start of the growth of silver bromide or silver iodobromide.
Silver bromide is preferably grown after the addition of a silver iodide fine grain emulsion. When silver iodobromide is used, the silver iodide content is 3 mol % or less with respect to the corresponding layer. Assume that the total silver amount of a completed tabular grain emulsion is 100, the silver amount of a layer grown after the addition of this silver iodide fine grain emulsion is preferably 5 to 50, and most preferably, 10 to 30. The temperature, pH, and pBr during the formation of this layer are not particularly restricted. However, the temperature is usually 40xc2x0 C. to 90xc2x0 C., and more preferably, 50xc2x0 C. to 80xc2x0 C., and the pH is usually 2 to 9, and more preferably, 3 to 7. In the present invention, the pBr at the end of the formation of the layer is preferably higher than that in the initial stages of the layer formation. Preferably, the pBr in the initial stages of the layer formation is 2.9 or less, and the pBr at the end of the layer formation is 1.7 or more. More preferably, the pBr in the initial stages of the layer formation is 2.5 or less, and the pBr at the end of the layer formation is 1.9 or more. Most preferably, the pBr in the initial stages of the layer formation is 1 to 2.3, and pBr at the end of the layer formation is 2.1 to 4.5. Dislocation lines are preferably introduced in the present invention by the above method.
In the formation of silver halide grains of the present invention, at least one of chalcogen sensiti-zation including sulfur sensitization and selenium sensitization, and noble metal sensitization including gold sensitization and palladium sensitization can be performed at any point during the process of preparing a silver halide emulsion. The use of two or more different sensitizing methods is preferable. Several different types of emulsions can be prepared by changing the timing at which the chemical sensitization is performed. The emulsion types are classified into: a type in which a chemical sensitization nucleus is embedded inside a grain, a type in which it is embedded in a shallow position from the surface of a grain, and a type in which it is formed on the surface of a grain. In emulsions of the present invention, the position of a chemical sensitization nucleus can be selected in accordance with the intended use. However, it is preferable to form at least one type of a chemical sensitization nucleus in the vicinity of the surface.
One chemical sensitization which can be preferably performed in the present invention is chalcogen sensitization, noble metal sensitization, or a combination of these. The sensitization can be performed by using active gelatin as described in T. H. James, The Theory of the Photographic Process, 4th ed., Macmillan, 1977, pages 67 to 76. The sensitization can also be performed by using any of sulfur, selenium, tellurium, gold, platinum, palladium, and iridium, or by using a combination of a plurality of these sensitizers at pAg 5 to 10, pH 5 to 8, and a temperature of 30xc2x0 C. to 80xc2x0 C., as described in Research Disclosure, Vol. 120, April, 1974, 12008, Research Disclosure, Vol. 34, June, 1975, 13452, U.S. Pat. Nos. 2,642,361,3,297,446, 3,772,031,3,857,711,3,901,714, 4,266,018, and 3,904,415, and British Patent 1,315,755. In the noble metal sensitization, salts of noble metals, such as gold, platinum, palladium, and iridium, can be used. In particular, gold sensitization, palladium sensitization, or a combination of the both is preferred. In the gold sensitization, it is possible to use known compounds, such as chloroauric acid, potassium chloroaurate, potassium aurithiocyanate, gold sulfide, and gold selenide. A palladium compound means a divalent or tetravalent salt of palladium. A preferable palladium compound is represented by R2PdX6 or R2PdX4 wherein R represents a hydrogen atom, an alkali metal atom, or an ammonium group and X represents a halogen atom, e.g., a chlorine, bromine, or iodine atom.
More specifically, the palladium compound is preferably K2PdCl4, (NH4)2PdCl6, Na2PdCl4, (NH4)2PdCl4, Li2PdCl4, Na2PdCl6, or K2PdBr4. It is preferable that the gold compound and the palladium compound be used in combination with thiocyanate or selenocyanate.
Examples of a sulfur sensitizer are hypo, a thiourea-based compound, a rhodanine-based compound, and sulfur-containing compounds described in U.S. Pat. Nos. 3,857,711, 4,266,018, and 4,054,457. The chemical sensitization can also be performed in the presence of a so-called chemical sensitization aid. Examples of a useful chemical sensitization aid are compounds, such as azaindene, azapyridazine, and azapyrimidine, which are known as compounds capable of suppressing fog and increasing sensitivity in the process of chemical sensitization. Examples of the modifier of chemical sensitization aid are described in U.S. Pat. Nos. 2,131,038, 3,411,914, and 3,554,757, JP-A-58-126526, and G. F. Duffin, Photographic Emulsion Chemistry, pages 138 to 143.
It is preferable to also perform gold sensitization for emulsions of the present invention. An amount of a gold sensitizer is preferably 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x927 mol, and more preferably, 1xc3x9710xe2x88x925 to 5xc3x9710xe2x88x927 mol per mol of a silver halide. A preferable amount of a palladium compound is 1xc3x9710xe2x88x923 to 5xc3x9710xe2x88x927 mol per mol of a silver halide. A preferable amount of a thiocyanide compound or a selenocyanide compound is 5xc3x9710xe2x88x922 to 1xc3x9710xe2x88x926 mol per mol of a silver halide.
An amount of a sulfur sensitizer with respect to silver halide grains of the present invention is preferably 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x927 mol, and more preferably, 1xc3x9710xe2x88x925 to 5xc3x9710xe2x88x927 mol per mol of a silver halide.
Selenium sensitization is a preferable sensitizing method for emulsions of the present invention. Known labile selenium compounds are used in the selenium sensitization. Practical examples of the selenium compound are colloidal metal selenium, selenoureas (e.g., N,N-dimethylselenourea and N,N-diethylselenourea), selenoketones, and selenoamides. In some cases, it is preferable to perform the selenium sensitization in combination with one or both of the sulfur sensitization and the noble metal sensitization.
In the present invention, a thiocyanate is preferably added before the addition of the aforementioned spectral sensitizing dyes and chemical sensitizers. A thiocyanate is preferably added after grain formation, and more preferably, after a desilvering step. Since a thiocyanate is preferably added during chemical sensitization, the addition of a thiocyanate is performed twice or more. Examples of a thiocyanate are potassium thiocyanate, sodium thiocyanate, and ammonium thiocyanate.
A thiocyanate is usually dissolved in an aqueous solution or a water-soluble solvent before being added. The addition amount is preferably 1xc3x9710xe2x88x925 to 1xc3x9710xe2x88x922 mol, and more preferably, 5xc3x9710xe2x88x925 to 5xc3x9710xe2x88x923 mol per mol of a silver halide.
It is advantageous to use gelatin as a protective colloid for use in preparation of emulsions of the present invention or as a binder for other hydrophilic colloid layers. However, another hydrophilic colloid can also be used in place of gelatin.
Examples of the hydrophilic colloid are protein, such as a gelatin derivative, a graft polymer of gelatin and another high polymer, albumin, and casein; sugar derivatives, such as cellulose derivatives, e.g., cellulose sulfates, hydroxyethylcellulose, and carboxymethylcellulose, soda alginate, and starch derivatives; and a variety of synthetic hydrophilic high polymers, such as homopolymers or copolymers, e.g., polyvinyl alcohol, polyvinyl alcohol with partial acetal, poly-N-vinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinylimidazole, and polyvinylpyrazole.
Examples of gelatin are lime-processed gelatin, acid-processed gelatin, and enzyme-processed gelatin described in Bull. Soc. Sci. Photo. Japan. No. 16, page 30 (1966). In addition, a hydrolyzed product or an enzyme-decomposed product of gelatin can also be used.
It is preferable to wash an emulsion of the present invention to form a newly prepared protective colloid dispersion for a desalting purpose. Although the temperature of washing can be selected in accordance with the intended use, it is preferably 5xc2x0 C. to 50xc2x0 C. Although the pH of washing can also be selected in accordance with the intended use, it is preferably 2 to 10, and more preferably 3 to 8. The pAg during washing is preferably 5 to 10, though it can also be selected in accordance with the intended use. The washing method can be selected from noodle washing, dialysis using a semipermeable membrane, centrifugal separation, coagulation precipitation, and ion exchange. The coagulation precipitation can be selected from a method using sulfate, method using an organic solvent, method using a water-soluble polymer, and method using a gelatin derivative.
In the preparation of the emulsion of the present invention, it is preferable to make salt of metal ion exist, for example, during grain formation, desalting, or chemical sensitization, or before coating in accordance with the intended use. The metal ion salt is preferably added during grain formation when doped into grains, and after grain formation and before completion of chemical sensitization when used to decorate the grain surface or used as a chemical sensitizer. The salt can be doped in any of an overall grain, only the core, the shell, or the epitaxial portion of a grain, and only a substrate grain. Examples of the metal are Mg, Ca, Sr, Ba, Al, Sc, Y, La, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ru, Rh, Pd, Re, Os, Ir, Pt, Au, Cd, Hg, Tl, In, Sn, Pb, and Bi. These metals can be added as long as they are in the form of salt that can be dissolved during grain formation, such as ammonium salt, acetate, nitrate, sulfate, phosphate, hydroxide, 6-coordinated complex salt, or 4-coordinated complex salt. Examples are CdBr2, CdCl2, Cd(NO3)2, Pb(NO3)2, Pb(CH3COO)2, K3[Fe(CN)6], (NH4)4[Fe(CN)6], K3IrCl6, (NH4)3RhCl6, and K4Ru(CN)6. The ligand of a coordination compound can be selected from halo, aquo, cyano, cyanate, thiocyanate, nitrosyl, thionitrosyl, oxo, and carbonyl. These metal compounds can be used either singly or in the form of a combination of two or more types of them.
The metal compounds are preferably dissolved in an appropriate solvent, such as methanol or acetone, and added in the form of a solution. To stabilize the solution, an aqueous hydrogen halogenide solution (e.g., HCl or HBr) or an alkali halide (e.g., KCl, NaCl, KBr, or NaBr) can be added. It is also possible to add acid or alkali if necessary. The metal compounds can be added to a reactor vessel either before or during grain formation. Alternatively, the metal compounds can be added to a water-soluble silver salt (e.g., AgNO3) or an aqueous alkali halide solution (e.g., NaCl, KBr, or KI) and added in the form of a solution continuously during formation of silver halide grains. Furthermore, a solution of the metal compounds can be prepared independently of a water-soluble salt or an alkali halide and added continuously at a proper timing during grain formation. It is also possible to combine several different addition methods.
It is sometimes useful to perform a method of adding a chalcogen compound during preparation of an emulsion, such as described in U.S. Pat. No. 3,772,031. In addition to S, Se, and Te, cyanate, thiocyanate, selenocyanic acid, carbonate, phosphate, and acetate can be present.
It is preferable to use an oxidizer for silver, in addition to a halogen oxoacid salt, during the process of preparing emulsions of the present invention. However, positive hole capturing silver nuclei obtained by reduction sensitization of the grain surface must remain to such an extent that the sensitivity/fog ratio is optimum in terms of photographic properties. A particularly effective compound is the one that converts those fine silver nuclei into silver ions, which are produced as a by-product in the processes of formation and chemical sensitization of silver halide grains and chemical sensitization, which do not contribute to an increase in the sensitivity, and which cause an increase in fog. The silver ions produced can form a silver salt hard to dissolve in water, such as a silver halide, silver sulfide, or silver selenide, or can form a silver salt easy to dissolve in water, such as silver nitrate.
Preferable oxidizers are an inorganic oxidizer of thiosulfonate and an organic oxidizer of quinones.
Photographic emulsions used in the present invention can contain various compounds in order to prevent fog during the preparing process, storage, or photographic processing of a sensitized material, or to stabilize photographic properties. That is, it is possible to add many compounds known as antifoggants or stabilizers, e.g., thiazoles such as benzothiazolium salt, nitroimidazoles, nitrobenzimidazoles, chlorobenzimidazoles, bromobenzimidazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, aminotriazoles, benzotriazoles, nitrobenzotriazoles, and mercaptotetrazoles (particularly 1-phenyl-5-mercaptotetrazole); mercaptopyrimidines; mercaptotriazines; a thioketo compound such as oxazolinethione; and azaindenes such as triazaindenes, tetrazaindenes (particularly 4-hydroxy-substituted(1,3,3a,7)tetrazaindenes), and pentazaindenes. For example, compounds described in U.S. Pat. Nos. 3,954,474 and 3,982,947 and JP-B-52-28660 can be used. One preferred compound is described in JP-A-63-212932. Antifoggants and stabilizers can be added at any of several different timings, such as before, during, and after grain formation, during washing with water, during dispersion after the washing, before, during, and after chemical sensitization, and before coating, in accordance with the intended application. The antifoggants and stabilizers can be added during preparation of an emulsion to achieve their original fog preventing effect and stabilizing effect. In addition, the antifoggants and stabilizers can be used for various purposes of, e.g., controlling the crystal habit of grains, decreasing the grain size, decreasing the solubility of grains, controlling chemical sensitization, and controlling the arrangement of dyes.
The above various additives can be used in the lightsensitive material according to the present technology, to which other various additives can also be added in conformity with the object.
The additives are described in detail in Research Disclosure Item 17643 (December 1978), Item 18716 (November 1979) and Item 308119 (December 1989), the disclosures of which are incorporated herein by reference. A summary of the locations where they are described will be listed in the following table.
With respect to the photographic lightsensitive material of the present invention and the emulsion suitable for use in the photographic lightsensitive material and also with respect to layer arrangement and related techniques, silver halide emulsions, dye forming couplers, DIR couplers and other functional couplers, various additives and development processing which can be used in the photographic lightsensitive material, reference can be made to EP 0565096A1 (published on October 13, 1993) and patents cited therein, all the disclosures of which are incorporated herein by reference. Individual particulars and the locations where they are described will be listed below.
1. Layer arrangement: page 61 lines 23 to 35, page 61 line 41 to page 62 line 14,
2. Interlayers: page 61 lines 36 to 40,
3. Interlayer effect imparting layers: page 62 lines 15 to 18,
4. Silver halide halogen compositions: page 62 lines 21 to 25,
5. Silver halide grain crystal habits: page 62 lines 26 to 30,
6. Silver halide grain sizes: page 62 lines 31 to 34,
7. Emulsion production methods: page 62 lines 35 to 40,
8. Silver halide grain size distributions: page 62 lines 41 to 42,
9. Tabular grains: page 62 lines 43 to 46,
10. Internal structures of grains: page 62 lines 47 to 53,
11. Latent image forming types of emulsions: page 62 line 54 to page 63 to line 5,
12. Physical ripening and chemical ripening of emulsion: page 63 lines 6 to 9,
13. Emulsion mixing: page 63 lines 10 to 13,
14. Fogged emulsions: page 63 lines 14 to 31,
15. Nonlightsensitive emulsions: page 63 lines 32 to 43,
16. Silver coating amounts: page 63 lines 49 to 50.
17. The additives are described in detail in Research Disclosure Item 17643 (December 1978), Item 18716 (November 1979) and Item 307105 (November 1989), the disclosures of which are incorporated herein by reference. A summary of the locations where they are described will be listed in the following table.
18. Formaldehyde scavengers: page 64 lines 54 to 57,
19. Mercapto-type antifoggants: page 65 lines 1 to 2,
20. Fogging agent, etc. releasing agents: page 65 lines 3 to 7,
21. Dyes: page 65, lines 7 to 10,
22. Color coupler summary: page 65 lines 11 to 13,
23. Yellow, magenta and cyan couplers: page 65 lines 14 to 25,
24. Polymer couplers: page 65 lines 26 to 28,
25. Diffusive dye forming couplers: page 65 lines 29 to 31,
26. Colored couplers: page 65 lines 32 to 38,
27. Functional coupler summary: page 65 lines 39 to 44,
28. Bleaching accelerator-releasing couplers: page 65 lines 45 to 48,
29. Development accelerator-releasing couplers: page 65 lines 49 to 53,
30. Other DIR couplers: page 65 line 54 to page 66 to line 4,
31. Method of dispersing couplers: page 66 lines 5 to 28,
32. Antiseptic and mildewproofing agents: page 66 lines 29 to 33,
33. Types of sensitive materials: page 66 lines 34 to 36,
34. Thickness of lightsensitive layer and swell speed: page 66 line 40 to page 67 line 1,
35. Back layers: page 67 lines 3 to 8,
36. Development processing summary: page 67 lines 9 to 11,
37. Developing solution and developing agents: page 67 lines 12 to 30,
38. Developing solution additives: page 67 lines 31 to 44,
39. Reversal processing: page 67 lines 45 to 56,
40. Processing solution open ratio: page 67 line 57 to page 68 line 12,
41. Development time: page 68 lines 13 to 15,
42. Bleach-fix, bleaching and fixing: page 68 line 16 to page 69 line 31,
43. Automatic processor: page 69 lines 32 to 40,
44. washing, rinse and stabilization: page 69 line 41 to page 70 line 18,
45. Processing solution replenishment and recycling: page 70 lines 19 to 23,
46. Developing agent built-in sensitive material: page 70 lines 24 to 33,
47. Development processing temperature: page 70 lines 34 to 38, and
48. Application to film with lens: page 70 lines 39 to 41
Moreover, preferred use can be made of a bleaching solution containing 2-pyridinecarboxylic acid or 2,6-pyridinedicarboxylic acid, a ferric salt such as ferric nitrate and a persulfate as described in EP No. 602,600, the disclosure of which is incorporated herein by reference. When this bleaching solution is used, it is preferred that the steps of stop and water washing be conducted between the steps of color development and bleaching. An organic acid such as acetic acid, succinic acid or maleic acid is preferably used in the stop solution. For pH adjustment and bleaching fog, it is preferred that the bleaching solution contains an organic acid such as acetic acid, succinic acid, maleic acid, glutaric acid or adipic acid in an amount of 0.1 to 2 mol/liter (hereinafter liter referred to as xe2x80x9cLxe2x80x9d).
Examples of the present invention will be described below. However, the present invention is not restricted to these examples.